How to Repair a Rotten Floor in a Bathroom

Object: To repair a rotten floor in a bathroom caused by a leaking commode, while saving hundreds of dollars by doing it yourself

Occasionally, a commode will have a slow leak not noticed for a long while and eventually the floor around the commode will rot. I have seen situations so bad that the commode would be leaning sideways. Following is the method I use when repairing rotten floors in rental houses where I do all the work myself, thus avoiding paying a professional hundreds of dollars to do perform the work.

The first thing to do is to remove the commode to a safe place out of the bathroom. You will have to turn off the water supply which is normally on the left side of the commode and usually about 4 to 6 inches above the floor. Next, follow the pipe from the cut-off up to the bottom of the commode tank. There you will find a large plastic or metal nut which is screwed onto a short pipe which sticks out of the bottom of the tank. You must unscrew this nut so that the tank is no longer attached to the water supply pipe. Following that you must remove the plastic caps which cover the bolts that hold the commode down to the floor. There will be two, one on each side. Your commode may not necessarily have the caps. Under the caps are brass nuts and bolts, typically ¼” or 5/16”. You will need to remove the nuts by unscrewing them with a wrench. In some cases, the nuts will not unscrew easily because of age, sediment, rust, etc. It may be necessary to grip the top of the bolt with some type of pliers. I use Vice Grip because they can be clamped very tightly on the bolt. By keeping the bolt from turning with the pliers, you may be able to unscrew the nut. Be aware that the pliers may damage the threads on the bolt, making it hard to complete the last few turns of the nut. At that point you may have to move the pliers to a position below the nut and continue to turn off the nut. In some cases, the installer may have used wood screws instead of bolts. In this case they usually are regular steel and will be very rusty and removal will be very difficult. In extreme cases, I may use a hacksaw or electric “sawsall” or jigsaw to cut out the bolts.

After disconnecting the water and getting the nuts off of the bolts, grab the commode by the bowl and lift it straight up off of the bolts. Without setting it down, carry it out of the bathroom to a safe place and place it on used cardboard or newspaper. The reason is that the bottom of the commode will have heavy wax stuck to it and it will damage carpet or other floor covering. Bear in mind that you need to remove all the water from both the tank and the bowl before attempting to move it. I use a simple plastic “squeeze” pump which can be found where Kerosene cans are sold. They are used to pump Kerosene from storage containers into Kerosene heaters. I’m sure other pumps will work. When no pump is available, I have used a small plastic cup to dip out the water from the bowl. When I can no longer get any out with the cup, I take a hand towel or wash cloth and soak up the water from the trap portion of the commode. If you don’t remove all the water, you will have a wet floor as soon as you move it. Don’t forget the water in the tank.

For the sake of this article, I am going to assume that the floor is not rotten underneath the tub or sink cabinet. The next thing that must be done is to clean off all the old wax which very likely will be nasty. This is most easily done with a putty knife about an inch wide. Scrape up all the old wax and deposit it in a grocery bag for disposal. Be sure to get the wax not only from the commode flange on the floor, but also the bottom of the commode.

With the commode out of the way, take a power saw and/or hammer and begin the process of cutting out the rotten floor material. Remove larger and larger pieces of the floor in an effort to get all the rotten wood out without getting much of the undamaged floor. I use a “sawsall” type of saw to cut out rotten wood right up next to a wall. I have also used a “skill” or circular saw and a jig saw. The “sawsall” doesn’t do the job as neatly, but it may be the only way to cut right up to the wall.

Once the entire rotten floor has been discovered and removed, use a square and cut out a rectangle of flooring, making sure that you cut into the undamaged wood, leaving your cuts as straight as possible, remembering that you eventually will have to cut and fit a new piece of wood to fit into the opening. Also, bear in mind that it is possible that the entire floor will have to be cut out, even the floor underneath the vanity cabinet, in which case it, too, would have to be removed.

Once the portion of floor has been removed, it may be necessary to replace the joists or main beams to which the floor is nailed because they, too, may have rotted. Most, if not all builders use untreated lumber to frame up a new house and use untreated plywood or chipboard for the floors-making it easier for the wood to rot if subjected to a continual leak of water. Therefore, to prevent this recurring, you should either replace the damaged joists or you should “scab onto” the old joists with new “treated wood” joists which can be found at any building supply firm. If the damage to the joists is not severe, meaning complete damage, then you may be able to cut a short length of new treated lumber and nail to the side of the old joist. Be sure to extend the new lumber at least a foot beyond the damaged area in both directions so that you have plenty of room to nail the new lumber to the unrotted portion of the old lumber.

After installing new joists, you will now need to replace the rotten floor which you previously cut out. Usually there are 2 layers of flooring, perhaps with a piece of tarpaper or plastic between them for a moisture barrier. You will need to take an accurate measurement of the thickness of each layer of flooring in an effort to find exact matches at the building supply house. For example, you may find that the sub floor (the one closest to the ground) is only ½” thick, while the main floor is ¾” thick. When you go to the building supply store, look for treated plywood to match the thickness of that which you have removed. It can usually be found in 2x2’, 2x4’, 4x4’ and 4x8’ sizes. You might have to buy more than one piece and fit them together like pieces of a puzzle to avoid having to buy a 4x8’ sheet. Obviously, the reason for buying treated plywood is to avoid the same rot event from occurring again in the future. Don’t forget to place a layer of tarpaper or plastic between the two pieces of plywood to serve as a moisture barrier. It may be a good idea to fasten the plywood down with stainless steel screws or special screws made just for the purpose of use in treated plywood. Regular nails will rust just like the untreated plywood and joists rotted.

Once all plywood has been fastened down, you will need to use wood filler which is a putty-like substance while in the container but hardens like wood when dry. Spread it into all the cracks between the old and new wood with a putty knife, leaving it has smooth and level as possible. Once it has dried, you will need to sand it down completely smooth with the surrounding surfaces so that when you run your hand over the seam, you can not tell the difference in the feel.

At this point, if you have not removed the old vinyl floor covering, it will be necessary to do so. Do some research to make sure that the flooring is not so old as to have asbestos in it. If it does, do not try to remove it yourself. There are two options if it has asbestos in it. One is to hire a professional which will be extremely expensive and one is to cover it with a thin sheet of plywood called “multiply”. Multiply comes in 4x4’ sheets and is marked with an “X” about every 4 inches in a grid. The “X” is where the nails are placed. Sometimes the multiply is necessary even if the vinyl does not contain asbestos. This might be the case when the vinyl is stuck so tightly to the existing floor that you can not get it all up without gouging holes in the plywood. Multiply gives you a new and smooth surface onto which you can place your new vinyl. It also raises the floor level by a ¼” making it necessary to add a metal trim edge at the doorway to transition to the floor level outside the doorway. I recommend replacing the vinyl with new vinyl which does not have to be glued down. Buy a size slightly larger than the room, place it in the room and straighten it to line up with the walls. Using a razor knife, cut the vinyl to just exactly fit the room. Be sure you have removed the shoe molding before doing this. New shoe molding will then cover your uneven cuts along the wall. Of course, you will need to cut out for the commode flange and the vanity. I use the piece cut out for the vanity inside the vanity as a waterproof barrier for the floor of the vanity. Trim it to fit also.

Finally you must re-install the commode, putting things back in the reverse order that you removed them. Be sure to purchase new brass bolts. Bolts come in two sizes; one is ¼” and one slightly stouter. I always like to get the stouter ones. This is one case where less is not more. Get the best bolts you can find because even they are not good enough. It is also advisable to replace the steel washers with new brass ones which you will have to purchase separately. Steel always rusts in the presence of water unless you opt for stainless. The bolts don’t come in stainless-just brass. Be sure to replace the old wax seal with a new one. It might be smart to purchase one with a built-in plastic “funnel” to help the water to go down the pipe instead of onto the floor. Wax seals come in several prices. Remember to buy quality products. While you’re into, it might also be a good idea to replace anything associated with the plumbing with new articles, such as the flapper in the tank. Flappers get old and rigid, thus causing a constant leak and water loss.

Of course, you may have to install new baseboard and shoe molding due to the damage you may have caused in removing the old molding. It’s always easier to replace the old with new while the room is torn out.